Various contemporary surgical procedures require aspiration of fluids that may contain solid or semi-solid tissue or other debris. In many cases, the fluids may need to be aspirated from a body cavity such as the lens capsule of the eye or a cavity in a joint such as the shoulder or the knee. It is typically desirable to maintain an ambient or a super-ambient pressure within the body cavity during such surgical procedures.
For example, the lens of a human eye may develop a cataracteous condition that affects a patient's vision. Cataracteous lenses are sometimes removed and replaced in a procedure commonly referred to as phacoemulsification. Phacoemulsification procedures are typically performed with an ultrasonically driven hand piece that is used to break the lens within the lens capsule of the eye. The broken lens is removed through an aspiration line that is coupled to the hand piece and protrudes into the lens capsule. The hand piece has a tip that is inserted through an incision in the cornea. The hand piece typically contains a number of ultrasonic transducers that convert electrical power into a mechanical oscillating movement of the tip. The distal end of the tip has an opening that is in fluid communication with the aspiration line. The distal end of the tip also has a sleeve that has an opening in fluid communication with an irrigation line. The irrigation line is typically connected to a bottle that can provide irrigation fluid to the surgical site. The oscillating movement of the tip breaks the lens into small pieces. The lens pieces and irrigation fluid are drawn into the aspiration line through the opening of the tip.
Phacoemulsification is more likely to be successful if ambient or super-ambient pressure can be maintained within the lens capsule and the anterior chamber of the eye during the procedure. However, vacuum surges can be created when the aspiration line is momentarily obstructed by solid or semi-solid tissue. Such vacuum surges can lead to transient aspiration flow rates through the aspiration line that substantially exceed the flow rate through the irrigation line and thereby cause a sub-ambient pressure to be momentarily applied to the surrounding tissue. The momentary sub-ambient pressure condition may cause an undesirable collapse of the anterior chamber of the eye, undesirable damage to the posterior aspect of the lens capsule of the eye, and/or endothelium cells to be undesirably drawn away from the cornea and towards the distal end the tip of the hand piece. On the other hand, too high an irrigation flow rate may undesirably move endothelium cells away from the cornea, or undesirably cause endothelium cells to be aspirated out of the eye.
Conventional phacoemulsification procedures are typically performed using a vacuum pressure of about 250 mmHg. There is a desire to increase the vacuum pressure to assist in aspirating larger pieces of the lens. Aspirating larger pieces would lower the amount of ultrasonic work that must be performed on the eye. Lowering the ultrasonic work would be desirable because ultrasound can irritate the eye. Consequently, there is a desire to create vacuums up to 500 mmHg to improve aspiration and reduce the amount of ultrasound delivered to the cornea. However, such higher pressures exacerbate the surgical risks associated with vacuum surges.
Also for example, some orthopedic medical procedures produce particles or other debris that must be removed from a cavity within a joint such as in the shoulder or knee. To remove such particles the surgeon may couple an aspiration tube to the surgical site. The aspiration tube, which pulls the debris from the body, is typically connected to a canister, which is connected to a suction tube connected to wall suction. To ensure that the surgical site is properly distended during surgery, relatively large quantities of irrigation fluid are typically introduced to the body to continuously irrigate the surgical site, and an infusion pump is typically required to offset the high flow created by the hospital vacuum line. The introduction of such amounts of irrigation fluid into the body can cause undesirable or excessive extravagation of irrigation fluid into the surrounding tissue. Also, vacuum surges can be created when the suction line is obstructed by solid or semi-solid tissue. Such vacuum surges can lead to transient aspiration flow rates through the hospital vacuum line that substantially exceed the flow rate of irrigation fluid and thereby cause a sub-ambient pressure to be momentarily applied to the surrounding tissue. The momentary sub-ambient pressure condition may cause partial collapse of the body cavity, damage to tissue near the distal end of the aspiration tube, and/or undesired tissue or fluid to be drawn towards the distal end of the aspiration tube.
Surgical aspiration systems may be designed to allow the surgeon to temporarily reverse the direction of aspiration flow by depressing a reflux bulb attached to the system. The surgeon may do this, for example, if tissue is drawn towards the distal tip of the aspiration tube or hand piece that the surgeon does not desired to be drawn (e.g. tissue that the surgeon does not want to be damaged by the distal tip). The surgeon may also initiate reflux to clear or dislodge an occlusion at the distal tip of the aspiration tube or hand piece.
Contemporary flow restrictors can limit the vacuum surges within the aspiration system, but only when the vacuum created by the vacuum pump is limited to a level that is safe in consideration of the diameter and length of that flow restrictor. For example, considering the typical dimensions of needles and tubings used in opthalmology, the flow that would be generated by a 500 mmHg vacuum is in excess of 250 cc/min, which could undesirably completely collapse an eye. Therefore, prior art systems that use a venturi pump must operate modest vacuum levels, e.g. below 200 mmHg unless very small needles are used. Such modest vacuum levels significantly limit the available un-occluded flow in such systems. Therefore, such flow restrictors are typically not used with peristaltic pumps that will significantly increase the pressure difference in response to an occlusion of the aspiration tip. The absence of pressure rise in response to occlusion in the contemporary aspiration systems limits their ability to aspirate large tissue particles. Also, an in-line flow restrictor may reduce the maximum flow rate in the absence of occlusion, even when the surgeon would prefer a higher flow rate to draw certain tissue towards the distal end of the tip (rather than moving the distal end of the tip towards the tissue). Also, an in-line flow restrictor can undesirably reduce the maximum reflux flow rate.
Therefore, it would be desirable to provide a surgical aspiration system that maintains an ambient or super-ambient pressure within a body cavity during a surgical procedure by limiting vacuum surges in the system. For example, it would be desirable to provide an aspiration system that is configured such that the flow rate out of the body cavity through the aspiration line does not greatly, or for a prolonged period, exceed the flow rate into the body cavity. In cataract surgery, for example, aspiration flow should be sufficient to quickly engage and aspirate lens particles from the eye, however in the event of an occlusion the high vacuum created in the aspiration line may temporarily produce too high a flow which could collapse the eye. Therefore, it would also be desirable to provide a surgical aspiration system that functions safely with limited or reduced flow rate of irrigation fluid through the irrigation line. It would also be desirable to provide an aspiration system that can safely take advantage of the use of a peristaltic pump (or another pump type that can significantly increase the relative vacuum response to an occlusion). It would also be desirable to provide an aspiration system that would allow a high aspiration flow rate in the absence of an occlusion, and a high reflux flow rate when needed by the surgeon.